Optically operating measuring devices are generally known. For example, German Patent Publication (DE-PS) No. 3,541,733 discloses an apparatus equipped with two optical resonators for measuring pressure. The optical resonators form the measuring element which is coupled to a laser light source and to an evaluating circuit. The optical resonators are formed by radiant index/light-wave conductor sections, arranged on the upper and lower sides of an elastic sensor body which is deformable by compression. A counteracting detuning of the resonators is produced by the application of compression to the sensor body, whereby the detuning is the measure of the applied pressure. However, such device is not suitable for measuring distances, since the attainable deflections do not yield an adequate range of measurement. The known pressure sensor operates as a Fabry-Perot device.